1. Field of the Invention
The present invention relates to a network printer apparatus and a LAN network system and, more particularly, to a network printer apparatus which realizes the communication function and a full-scale server function between the network printer apparatus and a LAN by adding a LAN adapter portion (Front End Processor)to the printer apparatus itself, and a LAN network system comprising such a network printer apparatus.
2. Description of the Related Art
A network printer apparatus is an apparatus connected to a plurality of personal computers or work stations through a LAN so as to store printing files (printing information) transferred from the personal computers or work stations in a storage unit, to register printing jobs in a printing job table, to form an image on the basis of the printing information which corresponds to the printing job, and to print the image on paper.
Such a conventional network printing apparatus executes printing operations in the order of receipt of printing information from a client or user (personal computer or work station).
The ways of description of printing data are different in personal computers or workstations which are produced by different makers. As a countermeasure, a network printer apparatus is provided with emulation programs for interpreting various types of printing data, and when printing information is transferred to the apparatus, the apparatus starts the emulation program designated by the printing information (emulation designation data) so as to interpret the printing data. In order to switch emulation programs, it is necessary to initialize the contents of the memory, which takes a considerable time.
The network printer apparatus has a printing function using a form overlay (a blank form, sometimes called merely overlay). This is a function of printing an image on paper overlayed with the form which is stored in advance. The form overlay is not constant but is changed in accordance with the printing job. When the overlay is changed, it is necessary to download the corresponding form overlay from a form overlay storing device of a hard disk or the like or a personal computer or the like for storing form overlays, which takes a considerable time.
When the printing jobs having the same emulation and the same overlay are executed in series, it is not necessary to change the emulation programs or overlays.
However, since personal computers or work stations made by different makers are connected to a LAN, and the form overlays differ with clients, it is scarcely the case that printing operations having the same printer emulation and the same form overlay are registered in series. It is therefore often necessary to switch emulation programs or change a form overlay for each printing job so that the efficiency of use of the network printer apparatus is lowered and the high speed printability of the apparatus is not fully utilized.
Information processing systems have changed from the processing form using a large computer system (mainframe) shown in FIG. 3a to a processing form using a PC/WS (personal computer/work station) as a nucleus shown in FIG. 3b. Referring to FIG. 3a, the symbol HST represents a large computer system, and DT designates a dumb terminal (nonintelligent terminal) connected to the large computer system.
As the processing form using a PC/WS as the nucleus, there are a stand-alone system and a network system in which a multiplicity of PCs/WSs are connected to a LAN network so as to constitute a network for the purpose of using resources and peripheral equipments in common. The stand-alone system is widely used by individuals and small-scale users, while the network system is widely used by large-scale users. FIG. 3b shows the stand-alone system comprised of individual dumb terminals each provided with a printer. The symbol PRT represents a printer connected to a PC/WS. In this system, each pair of PC/WS and printer is independent of another pair.
In the large computer system, one maker provides all equipments so as to sell the system in the market. In contrast, in the field of the LAN network system, various makers in the world compete with each other so as to sell a high-performance PC/WS at a low price in the market. In such a market environment, it is necessary to provide products which answer the needs for network, open system, downsizing and multivendor.
As shown in FIGS. 4a to 4c, in the conventional LAN network system, in a PC environment, PCs (personal computers) are connected to a LAN so as to constitute a network, in a WS environment, WSs (work stations) are connected to a LAN so as to constitute a network, and in a mixed environment, PCs and WSs connected to a LAN are now in wide use. Printers used in the mixed environment are connected in one of the forms (1), (2) and (3) as shown in FIG. 4(c). In the form (1), a printer PRT 1 may be locally connected to each of the PCs/WSs so as to print printing data supplied from the corresponding PC/WS. In the form (2), a printer PRT 2 is connected to a high-performance PC/WS as a host server SVR, and the PCs/WSs use the printer PRT2 connected to the server SVR in common. In the form (3), a printer PRT3 is connected to LAN via adapter AD and the PCs/WSs use the printer PRT3 connected to the LAN in common.
However, the conventional system in which printers are accommodated in a LAN network has the following problems.
(a) When printers are connected in the form (1), the availability of printers themselves is low, and since a printer is connected to each PC/WS, this system is disadvantageous in that the same number of printers as the number of PC/WS and the space for each printer are required.
(b) When a printer is connected in the form (2), printing data (e.g., complicated graphic design and graph) which takes a long time for producing an image exerts an influence on the CPU of the host server during the printing operation, which leads to a great deterioration of the performance of the host server.
(c) When a printer is connected in the form (3), if the PCs/WSs connected to the LAN network are produced by the same maker, in other words, the printing data have the same format, there is no problem. This is because the emulation program (e.g., Postscript and FM sequence) provided in the printer for interpreting the printing data can be used in common among the PCs/WSs. However, if the formats of the printing data are different and, hence, the emulation programs are different, a printing miss may sometimes be caused due to an interpretation miss of the printer.
In addition, when the communication protocol between the printer and a client is different, the printing data cannot be received from the client, so that the printing operation is impossible.
(d) With the spread of the LAN network, a vertical linkage, namely, the system in which a mainframe is connected to the LAN of PCs/WSs is used as well as a horizontal linkage, namely, the system in which PCs/WSs are connected to the LAN network. However, the format of the printing data in the mainframe is different from the format of printing data in PCs/WSs. It is therefore necessary to install a plurality of printers for printing the respective data. In other words, one printer cannot print all printing data required in such systems.
(e) With the development of printing technique, the printing using continuous paper has been replaced by the printing using cut paper. In response to the demand for the printing output which enables printing on a large number of sheets of paper in one cycle, a high-speed cut paper printer which is capable of printing 130 sheets/min has been realized. In such a high-performance in high-speed printer, since printing of a multiplicity of printing jobs is executed in a short time, it is necessary to identify printed cut paper for each printing job. For this purpose, a method of stacking printed cut paper in two alternate directions for each printing job is known and is referred to as offset stack. In this method, however, since the signals for stacking printed cut paper in one direction are alternately output, if only the stack of the printed paper for one printing job is taken out, the printed sheets of paper for the preceding and the subsequent printing jobs are stacked in the same direction, so that identification of a specific printing job is difficult. Thus, there is a problem in the post-processing mechanism of a high-speed printer, and a speedy solution thereof is demanded.
(f) The UNIX environment, i.e, the LAN network environment used in the related art has the following problems, and an amelioration is demanded.
When a printer is used as a remote printer (refer to FIG. 4(b)), a client is not fully informed of the end of the printing operation, details of a trouble caused in the printer or the like.
When a PC/WS such as a print server exclusively for controlling a printer is used, the system becomes expensive, so that a LAN network system which can dispense with a PC/WS server exclusively for a printer is highly demanded.
In the print server, a line command is used to request printing, enquire about a printing job, know the state of the printer, etc., so that expert knowledge is necessary. A LAN network environment which can be utilized without the need for expert knowledge is demanded.